The present invention relates generally to antennas, and more particularly to antennas used with wireless communicators.
Radiotelephones generally refer to communications terminals which provide a wireless communications link to one or more other communications terminals. Radiotelephones may be used in a variety of different applications, including cellular telephone, land-mobile (e.g., police and fire departments), and satellite communications systems. Radiotelephones must include an antenna for transmitting and/or receiving wireless communications signals.
Radiotelephones and other wireless communicators are undergoing miniaturization. Indeed, many contemporary radiotelephones are less than 11 centimeters in length. As a result, there is increasing interest in small antennas that can be internally mounted within the housings of radiotelephones so as not to be visible to users.
In addition, it may be desirable for radiotelephones to operate within multiple frequency bands in order to utilize more than one communications system. For example, GSM (Global System for Mobile) is a digital mobile telephone system that typically operates at a low frequency band (frequency band of operation: 880-960 MHz). DCS (Digital Communications System) is a digital mobile telephone system that typically operates at high frequency bands (frequency band of operation: 1710-1880 MHz). The frequency bands allocated in North America are 824-894 MHz for Advanced Mobile Phone Service (AMPS) and 1850-1990 MHz for Personal Communication Services (PCS). Accordingly, internal antennas, such as inverted-F antennas are being developed for operation within multiple frequency bands.
Inverted-F antennas may be well suited for use within the confines of radiotelephones, particularly radiotelephones undergoing miniaturization. As is well known to those having skill in the art, conventional inverted-F antennas include a conductive element that is maintained in spaced apart relationship with a ground plane. Exemplary inverted-F antennas are described in U.S. Pat. Nos. 5,684,492 and 5,434,579 which are incorporated herein by reference in their entirety.
Unfortunately, conventional inverted-F antennas typically resonate within narrow frequency bands. In addition, conventional inverted-F antennas may occupy more volume as compared with other types of antennas. As such, a need exists for small, internal radiotelephone antennas that can operate within multiple frequency bands.
In view of the above discussion, multi-frequency band antennas for use within wireless communicators, such as radiotelephones, according to embodiments of the present invention, include a first conductive branch that is configured to radiate in a first frequency band and a second conductive branch that is configured to radiate in a second frequency band that is different from the first frequency band. The first conductive branch includes opposite first and second end portions and opposite first and second edge portions that extend between the first and second end portions. A notch may be formed in the second edge portion adjacent the second end portion. The second conductive branch includes opposite third and fourth end portions and opposite third and fourth edge portions that extend between the third and fourth end portions. The first and second conductive branches are connected together at the first and third end portions and are configured to electrically couple at the respective second and fourth end portions. Coupling is utilized between the first and second conductive branches to achieve bandwidth and gain results desired for the antenna.
A first conductive element having a free end extends from the third edge portion of the second conductive branch adjacent the fourth end portion. The first conductive element free end is spaced-apart from the second edge portion of the first conductive branch by a distance of less than about ten millimeters (10 mm) and preferably less than about five millimeters (5 mm). The notch is in adjacent, spaced-apart relationship with at least a portion of the first conductive element free end and facilitates electrical coupling between the first and second conductive branches so as to enhance radiation efficiency in at least one of the first and second frequency bands.
A second conductive element extends from the first edge portion of the first conductive branch adjacent the first end portion and includes a wireless communications signal feed terminal and a ground feed terminal. A third conductive element extends from the first edge portion of the first conductive branch at an intermediate location between the first and second end portions. The third conductive element is configured to tune the first frequency band. A fourth conductive element extends from the third end portion of the second conductive branch and is configured to tune both the first and second frequency bands. A fifth conductive element extends from the fourth end portion of the second conductive branch and is configured to tune the second frequency band.
Antennas according to embodiments of the present invention are configured to be disposed on and/or within dielectric substrates and mounted internally within wireless communicators, such as radiotelephones, in adjacent, spaced-apart relationship with a ground plane. The inside surface of a wireless communicator housing may serve as a substrate and antennas according to embodiments of the present invention may be printed on the housing surface. A foam material may also serve as a substrate according to embodiments of the present invention.
Antennas according to embodiments of the present invention may be particularly well suited for use within wireless communicators, such as radiotelephones, wherein space limitations may limit the performance of internally mounted antennas. Moreover, antennas according to embodiments of the present invention may be particularly well suited for operation within multiple frequency bands.